Rubber vulcanizing agentIncluding elemental sulfur, seleniumtellurium, sulfur compounds,peroxide，Quinones，Amine compounds，Resin compounds，metallic oxideAnd isocyanates, etc.Most commonly usedElemental sulfurandSulfur compounds。The most commonly used are elemental sulfur and sulfur compounds.[1]
Vulcanization principle
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Dry sulfuration in catalyst is carried out in the high-pressure circulating loop composed of heating, reaction, heat exchange, cooling, high-pressure separation, circulating hydrogen compressor and logistics pipeline of hydrocracking.The procedure includes: using the circulating hydrogen heated by the heating furnace, heating the catalyst according to the maximum circulating hydrogen flow rate and the required heating rate, injecting the vulcanizing agent (DMDS) into the inlet of the reaction heating furnace according to the strictly controlled flow rate, and using the vulcanizing agent to decompose the H2S vulcanizing catalyst generated in the presence of hydrogen.When the catalyst is presulfurized, the following two main reactions will occur in the reactor:
(1) The vulcanizing agent (DMDS) first reacts with hydrogen to produce hydrogen sulfide and methane, which is an exothermic reaction.This reaction generally occurs at the inlet of refining reactor R101, and the reaction speed is fast.
(2) Oxidized catalyst active components (nickel oxide, molybdenum oxide, etc.) and hydrogen sulfide react to become sulfurized catalyst active components. The reaction is exothermic and occurs on each catalyst bed in the reactor.The temperature rise during presulfiding is caused by this reaction.
(3) According to the above chemical reaction equation and the content of active metal components in the catalyst, the theoretical amount of vulcanizing agent and the theoretical amount of generated water required for complete vulcanization of unit catalyst can be calculated.
There may also be undesirable side reactions in the sulfuration process: the active components of the catalyst in the oxidized state (nickel oxide, molybdenum oxide, tungsten oxide) are reduced by hydrogen to generate metal elements and water, which will greatly damage the activity of the catalyst.This reaction is extremely harmful and should be avoided as far as possible.The higher the temperature (above 230 ℃), the easier this side reaction will occur in the presence of hydrogen and without hydrogen sulfide.
The curing process mainly passes through two constant temperature stages of 230 ℃ and 370 ℃.The degree of completion of vulcanization is generally subject to that the amount of vulcanizing agent added in the whole process reaches 120% of the theoretical sulfur content of the catalyst calculated according to the metal.The constant temperature time can be determined by measuring the hydrogen sulfide concentration at the reactor outlet.Before the constant temperature of 230 ℃, hydrogen sulfide must completely penetrate the catalyst bed (marked by the beginning of a large amount of hydrogen sulfide in the circulating hydrogen).The final curing temperature is generally 360 ℃ - 370 ℃.In fact, there is an equilibrium limit value at each temperature. Even if the vulcanization time is prolonged, the sulfur content will not increase. When the temperature is above 300 ℃, the vulcanization reaction speed is fast, and the vulcanization can be completed.[2]
synthetic route
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With mercaptan as raw material
Mercaptan is one of the main raw materials for synthesis of vulcanizing agent. Mercaptan can be used in alkali metalalkaline-earth metalOfhydroxideAnd react with oxygen to obtain vulcanizing agent.It can also be mixed with elemental sulfur as raw material to synthesize organic sulfide under the action of alkaline catalyst.The first catalysts used in this synthesis route are amine, alkanolamine, mercaptan salt, alcohols and inorganic bases. However, the use of these catalysts has some shortcomings, such as low yield, low product purity, and unpleasant smell.Therefore,New catalystThe key point of this synthetic route is the research of.The alkene oxide group in the composition is replaced by epoxane, so thatPolysulfideThe yield of the product is further improved, the chroma becomes lower, and the chroma is less than or equal to, and the product has no unpleasant smell or turbidity.Some scholars began to use resin as catalyst.It is proposed to use organic compounds containing quaternary or tertiary amine groupsAnion exchange resinAs a catalyst, this resin exists in the reaction system in the form of beads or double teeth, with low solubility and easy recycling, but the yield of organic vulcanizing agent is not high.In order to solve this problem, the first research was carried out, and the resin with one or one form was proposed as the catalyst.This kind of resin has a highly cross-linked macroporous structure. Compared with gel type resin, it has greater catalytic activity in the reaction process and can effectively improve the yield of organic vulcanizing agent.Aretz proposed to usepolystyreneoneDivinylbenzeneA resin is used as catalyst, which can make low-grade organicDisulfideAnd polysulfide react with sulfur element to obtain advanced polysulfide.In addition, the resin can also make senior organic vulcanizing agent react with mercaptan to obtain lower polysulfide.The resin exists in the reaction liquid in the form of granules or beads, and is easy to be separated after the reaction.Fremi has developed a resin based on polystyrene divinylbenzene, which is grouped by ethylene diamine or polyethylene polyamine. The catalyst can effectively improve the conversion rate of reactants.The application of these new catalysts not only effectively improves the sulfur content of vulcanizing agent, but also widens the range of raw materials. More importantly, it overcomes the shortcomings of low yield of traditional catalysts, low product purity, and unpleasant smell.However, the synthesis of new catalysts is complex, the cost of raw materials is too high, and some raw materials are not easy to obtain, which is not easy to be industrialized.[1]
With olefins and sulfur
The reaction mechanism of sulfur and olefins to synthesize organic vulcanizing agent is that in the presence of catalyst, at a certain temperature, the ring breaks to form linear molecules, which exist in the system in the form of free radicals, and react with olefins to generate organic vulcanizing agent.The synthesis of organic vulcanizing agents from sulfur and olefins is the most widely used and has been highly valued by scholars.The patent discloses the synthesis of organic vulcanizing agent using sulfur and isobutene as raw materials. The organic vulcanizing agent synthesized by this method has small odor, less by-products and no pollution.However, this method is not suitable for industrial application because of its harsh reaction conditions and high cost.The patent discloses the direct reaction of elemental sulfur and olefin to synthesize vulcanizing agent. The process of synthesizing organic vulcanizing agent by this method is simple, but there are many by-products with unpleasant odor, and some by-products are corrosive, causing serious damage to equipment.In view of the above problems, Sun Laiyin proposed to use isobutene as the raw material to synthesize organic vulcanizing agent under high pressure. This method has few by-products, small smell, almost no pollution to the environment, high sulfur content, but isobutene is not easy to obtain, and the price is high.Ji Yonggang proposed to use butene, a byproduct with low utilization rate in the separation of butene, as the raw material for the synthesis of vulcanizing agent. This method is simple in synthesis process, cheap and easy to obtain raw materials, and greatly reduces the production cost.Although several compounds with different sulfur content can be obtained by synthesizing organic vulcanizing agent from a single olefin, the problem of exothermic concentration still exists when the catalyst is presulfurized.In order to solve this problem, many scholars proposed to use mixed vulcanizing agent to presulfurize the catalyst, but the proportion of each component of the mixed vulcanizing agent is not easy to determine, the cost is high, and there are many by-products during presulfurization.Yu Shouzhi uses the distillate oil generated from wax cracking as the raw material for the synthesis of organic vulcanizing agent. This method solves the problem of centralized heat release of single polysulfide during pre vulcanization, but the product has a large anvil and poor mobility, so it needs to be diluted before pre vulcanization.Wang Deqiu proposed to use distillate oil as raw material to synthesize organic vulcanizing agent. The organic vulcanizing agent synthesized by this method has high sulfur content, low toxicity, small immunity and good fluidity.Synthesis route with sulfur, hydrogen sulfide and olefin as raw materials Organic vulcanizing agent is prepared with sulfur, olefin and hydrogen sulfide as raw materials.[1]
Olefins, sulfur halides
Using olefins and sulfur halides as raw materials to synthesize vulcanizing agents is a common method in China's industry.Sulfur halide and olefin can generate halogen containing organic sulfide in the presence of catalyst, and then obtain organic sulfide through dehalogenation process.In the early s of the th century, Chinese scholar Huang Jinxia proposed to use sulfur chloride and isobutene as raw materials to synthesize organic vulcanizing agent. The organic vulcanizing agent synthesized by this method has high sulfur content, high stability and low corrosivity, but this method will produce a large amount of waste gas, wastewater and waste liquid in the production process of organic vulcanizing agent to pollute the environment.In recent years, many literatures have reported the improvement method of this synthesis route successively. For example, Yang Jingpei proposed to synthesize the organic sulfide containing impurities in two steps under the closed pipeline, and then obtain the pure organic sulfide through separation, dehydration, refining and other steps.This process is carried out in a closed pipeline to avoid environmental pollution caused by waste gas and liquid waste.However, this method is not suitable for industrial application because of its complex synthesis process and high requirements for equipment.Zhou Bo proposed to treat sulfurized isobutene containing chlorine atoms by twice adding sulfur and dechlorination. This method simplifies the process steps, saves costs, but has a long production cycle.Qi Xiangyang proposed to recycle the sulfur-containing waste liquid generated from the second step of sulfuration and dechlorination reaction for the next first step of sulfuration and dechlorination reaction, which not only reduces the discharge of waste liquid, but also saves production costs.The new synthesis process solves the problem of "three wastes" and reduces the production cost, but it is difficult to realize industrial application due to large equipment investment, long production cycle and complex operation process.[1]
Rubber vulcanizing agent
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The materials that can vulcanize rubber under certain conditions are collectively called vulcanizing agents. The so-called vulcanization is to make the linear molecular structure of rubber become a three-dimensional network structure through the "bridge" of the vulcanizing agent, so that the mechanical and physical properties of rubber can be significantly improved.
1. Sulfur: yellow solid material, widely used inNatural rubberAnd partssynthetic rubberMedium.Commonly used sulfur includes sulfur powder, sublimed sulfur (also called sulfur bloom) and precipitated sulfur.Sulfur is insoluble in water, slightly soluble in ethanol and ether, and soluble incarbon disulfideandcarbon tetrachloride。It is characterized by low heat resistance, high strength and corrosion to copper wires of vulcanized rubber. It is suitable for natural rubber and some synthetic rubber.In the wire and cable rubber formula, the amount of sulfur is about 0.2 to 5 parts, but the amount of sulfur can be reduced due to the addition of accelerator.
The specific gravity of zinc oxide is 5.6, which is a white powder, non-toxic and tasteless.Zinc oxide is widely used in rubberNeopreneIt is often used with magnesium oxide as the main curing agent.stayNatural rubberIt can be used as activator of accelerator in other olefin rubber.In addition, it also has a reinforcing effect.It plays the role of shielding ultraviolet ray in the rubber resistant to sunlight aging.Zinc oxide in natural rubber andbutyl rubber The medium dosage is 5~10 parts, and the general dosage of chloroprene rubber mixed with magnesium oxide is 5 parts.
Magnesium oxide is used as a secondary vulcanizing agent in chloroprene rubber, which can prevent the advance vulcanization of chloroprene rubber when mixing.This product can improve the tensile strength, constant elongation strength and hardness of neoprene.It can neutralize a small amount of hydrogen sulfide produced by halogenated rubber during vulcanization or under other oxidation conditions.The chlorosulfonated polyethylene rubber can give it good physical and mechanical properties, especially small permanent deformation.However, the water resistance is poor.The general dosage is 3~7 portions.Magnesium oxide is a white loose powder with a specific gravity of 3.2, which can gradually absorb water andcarbon dioxideIt becomes alkali or magnesium carbonate, which reduces the activity, so it should be kept tightly sealed.
3. Resin curing agent: resin curing agent is mainly thermosetting alkyl phenolic resin and epoxy resin.Vulcanization of unsaturated carbon chain rubber andbutyl rubber It can significantly improve the heat resistance of vulcanizate.The main varieties commonly used are phenol formaldehyde resin, such as tert butyl phenol formaldehyde resin and tert octyl phenol formaldehyde resin.Effect of epoxy resin on carboxyl rubber andNeopreneThe vulcanized rubber has good bending resistance.
4. Thuram: full nameTetramethyl thiuram disulfide, the trade name is TMTD.It is a widely used vulcanizing agent in wire and cable rubber, and can also be used asVulcanization accelerator。The pure product has a melting point of 147 ℃~148 ℃, a specific gravity of 1.29, and is a gray white powder.It isNatural rubberIt can be decomposed into free radicals at 100 ℃, so it can be used for rubber crosslinking.The heat resistance and aging resistance of rubber can be improved by using thiuram as vulcanizing agent.The vulcanization curve is flat and not easy to burn.Suitable for natural rubberbutadiene styrene rubber、Nitrile rubberAnd all unsaturated rubbers containing double bonds.In general heat-resistant rubber, the amount of thiuram is 2-3 parts, while in continuous vulcanized rubber formula, the amount is 2-5 parts, and the amount used as accelerator is 0.3-0.5 parts.[2]
